Electrical devices often comprise cables which extend from one printed circuit board to another or from a printed circuit board to an electrical component. In many instances, the cable is a flat flexible cable having a plurality of generally parallel conductors with flexible insulation disposed around and between the respective conductors. In some instances, an electrical connector with terminals therein is mounted to the printed circuit board, such that the terminals of the connector are electrically connected to the conductive areas on the circuit board. A cable then may be terminated to a second electrical connector which can be mated to the board-mounted connector. Connections of this type are employed when it is necessary to periodically separate the cable from the circuit board. However, these mateable pairs of connectors are relatively expensive and can represent a substantial cost penalty in the highly competitive electronics industry. As a result, it is desirable to directly and permanently connect the conductors of the cable to the conductive areas on the circuit board in situations where periodic disconnection will not be required. This direct connection of the cable to the circuit board can result in substantial cost savings and manufacturing efficiencies. In particular, the respective conductive leads of the cable can be soldered directly to the conductive areas on the circuit board without mateable pairs of terminals and connector housings.
The direct connection of the conductive leads in the cable to the conductive areas on the circuit board must provide for strain relief. In particular, stresses exerted on the cable either during assembly of the electrical apparatus or during use of the apparatus may create strains that could damage the soldered connection between the leads of the cable and the conductive areas on the circuit board.
U.S. Pat. No. 4,886,942 to Lenz et al., dated Dec. 12, 1989 and assigned to the assignee of this invention, discusses prior art relating to structures to provide strain relief for direct cable to circuit board electrical connections. The Lenz et al. patent discloses a new and improved strain relief structure which has various stated advantages over the prior art. Specifically, the Lenz et al. patent is directed to a strain relief structure comprising a body having at least one slot or aperture for receiving a cable therein. The cable may be prepared or stripped prior to insertion into the strain relief structure such that the terminal portions of the conductive leads are exposed for subsequent electrical connection to conductive areas on a circuit board. The cable may be a flat flexible cable having a plurality of conductive leads disposed in a parallel array. The preparation of the end of the flat flexible cable may comprise removing portions of the insulation between the cables for a selected distance from the end of the cable. Thus, the extreme end of the flat flexible cable may have all insulation stripped away such that the uninsulated conductive leads extend from the end of the cable. A portion of the flat flexible cable adjacent the stripped end may include insulation around each individual conductive lead, but with the insulation webs between adjacent leads at least partly removed.
The strain relief structure of the Lenz et. al. patent comprises at least one strain relief means extending into the cable receiving slot or aperture. The strain relief means may be angularly aligned with respect to the direction of insertion to be deflected by the insertion of the cable into the slot or aperture. However, the angular alignment and the configuration of the strain relief means enables engagement of the insulation on the cable to substantially prevent withdrawal of the cable and provide strain relief. The strain relief means may comprise at least one deflectable finger.
The strain relief structure of the Lenz et. al. patent can be employed by mounting the cable and the strain relief structure to one another prior to mounting on a circuit board. In particular, the prepared cable and the strain relief structure can be shipped and/or stored in an initially assembled condition prior to mounting of the cable and strain relief structure on a circuit board. Additionally, the strain relief means of the structure will have already engaged the cable to prevent unintended separation of the strain relief structure from the cable prior to installation on the circuit board.
The initially assembled cable and strain relief structure then can be securely mounted to the circuit board with the leads of the cable in a protected properly aligned condition relative to the conductive areas, through holes or other such conductive lead receiving means on the circuit board. The strain relief structure thus ensures proper alignment of the exposed conductors during installation on the circuit board and greatly facilitates component assembly.